A colourless salt (X) is soluble in water and also in alcohol and amines. On strong heating, (X) gives a brown gas (Y) and a grey residue. (X) dissolves in ammonia to give a solution (Z) which gives silver mirror with aldehydes. A solution of (X) is easily reduced by iron (II) sulphate. A solution of (X) also gives a brick red precipitate with potassium dichromate solution. Hence, choose the correct alternative: